U.S. patent application number 09/899697 was filed with the patent office on 2002-04-25 for method and apparatus for shaping semiconductor surfaces.
Invention is credited to Wipiejewski, Torsten.
Application Number | 20020048956 09/899697 |
Document ID | / |
Family ID | 7893558 |
Filed Date | 2002-04-25 |
United States Patent
Application |
20020048956 |
Kind Code |
A1 |
Wipiejewski, Torsten |
April 25, 2002 |
Method and apparatus for shaping semiconductor surfaces
Abstract
A method and an apparatus for shaping semiconductor surfaces, in
which a semiconductor wafer with a surface to be shaped is clamped
in-between two plates. In which case at least one plate has a
negative form with respect to the desired form to be formed in a
semiconductor surface and the semiconductor surface is pressed by
the plates at an elevated temperature. The method can be used
particularly advantageously for fabricating concave microlens
structures in semiconductor surfaces.
Inventors: |
Wipiejewski, Torsten; (Santa
Barbara, CA) |
Correspondence
Address: |
LERNER AND GREENBERG, P.A.
PATENT ATTORNEYS AND ATTORNEYS AT LAW
Post Office Box 2480
Hollywood
FL
33022-2480
US
|
Family ID: |
7893558 |
Appl. No.: |
09/899697 |
Filed: |
July 5, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09899697 |
Jul 5, 2001 |
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PCT/DE00/00009 |
Jan 3, 2000 |
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Current U.S.
Class: |
438/691 |
Current CPC
Class: |
H01L 21/67092
20130101 |
Class at
Publication: |
438/691 |
International
Class: |
H01L 021/461; H01L
021/302 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 4, 1999 |
DE |
199 00 051.4 |
Claims
I claim:
1. A method for shaping semiconductor surfaces, which comprises the
steps of: providing a semiconductor wafer having a semiconductor
surface to be shaped and formed of a compound semiconductor
material; clamping the semiconductor wafer in-between two plates,
at least one of the plates having a negative form with respect to a
desired form to be formed in the semiconductor surface; pressing
the semiconductor surface using the two plates at an elevated
temperature; and carrying out the method in an atmosphere enriched
with an element of the compound semiconductor material.
2. The method according to claim 1, which comprises forming a first
plate of the two plates with the negative form for producing the
desired form in the semiconductor surface of the semiconductor
wafer and forming a second plate of the two plates with a planar
area.
3. The method according to claim 1, which comprises exerting a
pressure, to obtain a pressing action, on at least one of the two
plates in a direction perpendicular to the semiconductor wafer.
4. The method according to claim 3, which comprises exerting the
pressure on both of the two plates in the direction perpendicular
to the semiconductor wafer.
5. The method according to claim 3, which comprises setting the
pressure to be greater than 1 MPa and the elevated temperature to
be greater than 600.degree. C.
6. The method according to claim 1, which comprises selecting the
atmosphere from the group consisting of an inert gas atmosphere, a
protective-gas atmosphere, a nitrogen gas atmosphere and an argon
gas atmosphere.
7. The method according to claim 6, which comprises: using GaAs as
the compound semiconductor material; and selecting the atmosphere
to be enriched with arsenic.
8. A method for fabricating a light-emitting diode, which comprises
the steps of: providing a semiconductor wafer having a
semiconductor surface to be shaped; clamping the semiconductor
wafer in-between the two plates, at least one of the plates having
a negative form with respect to a desired form to be formed in the
semiconductor surface; pressing the semiconductor surface using the
two plates at an elevated temperature, resulting in a structure
having at least one curved depression produced in the semiconductor
surface; growing an active layer sequence on a section containing
the curved depression; and providing the structure with electrical
contacts.
9. The method according to claim 8, which comprises forming the
structure as a microlens.
10. The method according to claim 8, which comprises forming a
first plate of the two plates with the negative form for producing
the desired form in the semiconductor surface of the semiconductor
wafer and forming a second plate of the two plates with a planar
area.
11. The method according to claim 8, which comprises exerting a
pressure, to obtain a pressing action, on at least one of the two
plates in a direction perpendicular to the semiconductor wafer.
12. The method according to claim 11, which comprises exerting the
pressure on both of the two plates in the direction perpendicular
to the semiconductor wafer.
13. The method according to claim 11, which comprises setting the
pressure to be greater than 1 MPa and the elevated temperature to
be greater than 600.degree. C.
14. The method according to claim 8, which comprises carrying out
the method in an atmosphere selected from the group consisting of
an inert gas atmosphere, a protective-gas atmosphere, a nitrogen
gas atmosphere and an argon gas atmosphere.
15. The method according to claim 14, which comprises: using GaAs
as the compound semiconductor material; and selecting the
atmosphere to be enriched with arsenic.
16. The method according to claim 8, which comprises forming the
negative form to have convex structures for producing concave
structures in the semiconductor surface.
17. The method according to claim 8, which comprises growing a
Bragg reflector layer sequence before performing the step of
growing the active layer sequence on the section containing the
curved depression.
18. The method as claimed in claim 17, which comprises growing a
further Bragg reflector layer sequence after the step of growing
the active layer sequence on the section containing the curved
depression resulting in a vertical resonator laser diode being
produced.
19. An apparatus for shaping semiconductor surfaces, comprising:
two plates, at least one of said two plates having a negative form
with respect to a desired form to be formed in a semiconductor
surface of a semiconductor wafer; a pressing apparatus for exerting
a pressure on at least one of said two plates in a direction
perpendicular to the semiconductor wafer disposed between said two
plates; and dome-shaped structures for distributing a compressive
force disposed on that side of said two plates being remote from
the semiconductor wafer.
20. The apparatus according to claim 19, wherein said two plates
include a first plate having the negative form and a second plate
with a planar area.
21. The apparatus according to claim 19, wherein said two plates
are formed of a material, and at a shaping temperature, the
semiconductor wafer to be pressed has a lower hardness than said
material of said two plates.
22. The apparatus according to claim 19, wherein said two plates
are formed of a material selected from the group consisting of
silicon, metal, and molybdenum.
23. An apparatus for shaping semiconductor surfaces, comprising:
two plates, at least one of said two plates having a curved
elevation shaped for producing a curved depression; and a pressing
apparatus for exerting a pressure on at least one of said two
plates in a direction perpendicular to a semiconductor wafer
disposed between said two plates for forming the curved depression
in a semiconductor surface of the semiconductor wafer.
24. The apparatus according to claim 23, wherein said two plates
include a first plate having said curved elevation being a negative
form with respect to a desired form to be formed in the
semiconductor surface of the semiconductor wafer and a second plate
with a planar area.
25. The apparatus according to claim 23, wherein said two plates
are formed of a material, and at a shaping temperature, the
semiconductor wafer to be pressed has a lower hardness than said
material of said two plates.
26. The apparatus according to claim 23, wherein said two plates
are formed of a material selected from the group consisting of
silicon, metal, and molybdenum.
27. The apparatus according to claim 23, including dome-shaped
structures for distributing a compressive force disposed on a side
of said two plates which is remote from the semiconductor wafer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to a method for shaping semiconductor
surfaces and an apparatus for carrying out the method.
[0003] Optical microcomponents such as e.g. microlenses and
microlens arrays have been used for many years in optoelectronics.
Convex microlenses can be produced in a particularly simple manner
using resoftened photoresist structures (photoresist reflow). The
convex forms form automatically during heating as a result of the
surface tension in the photoresist and can be transferred by dry
etching methods e.g. in silicon semiconductor wafers. The
reproducible fabrication of concave structures is significantly
more difficult, because a self-aligning photoresist process such as
reflow is not available. However, concave microlenses could
advantageously be used in numerous applications, such as e.g. for
correcting the astigmatism of the output radiation of edge-emitting
laser diodes. Usually, an attempt is made to produce concave
structures by wet-chemical etching methods utilizing diffusion
effects. Owing to poor reproducibility and inadequate surface
quality, such methods have not, to date, gained admittance to
applications on an industrial scale.
[0004] U.S. Pat. No. 5,378,289 describes a method for shaping a
semiconductor surface in which a surface made of an amorphous
silicon is simultaneously deformed and crystallized by a textured
pressure mold which is made of a crystalline silicon and is
provided with pyramids being pressed into the amorphous silicon
surface under the action of heat. This makes it possible to
fabricate a crystalline silicon film that has a textured surface
corresponding to the textured surface of the mold used for the
pressing process.
SUMMARY OF THE INVENTION
[0005] It is accordingly an object of the invention to provide a
method and an apparatus for shaping semiconductor surfaces which
overcome the above-mentioned disadvantages of the prior art methods
and devices of this general type, which specifies a simple and
cost-effective method which can be used to achieve the shaping of
semiconductor surfaces. In particular, it is an object of the
present invention to produce concave surface structures by a method
of this type.
[0006] With the foregoing and other objects in view there is
provided, in accordance with the invention, a method for shaping
semiconductor surfaces. The method includes the steps of providing
a semiconductor wafer having a semiconductor surface to be shaped
and formed of a compound semiconductor material and clamping the
semiconductor wafer in-between two plates. At least one of the
plates has a negative form with respect to a desired form to be
formed in the semiconductor surface. The semiconductor surface is
pressed by the two plates at an elevated temperature and the method
is carried out in an atmosphere enriched with an element of the
compound semiconductor material.
[0007] Accordingly, the present invention relates to a method for
shaping semiconductor surfaces, in which a semiconductor wafer with
a surface to be shaped is clamped in between the two plates. In
which case at least one plate has a negative form with respect to
the desired form of the semiconductor surface, and the
semiconductor surface is pressed by the plates at an elevated
temperature.
[0008] Preferably, in this case a first plate has the negative form
with respect to the desired form of the semiconductor surface and a
second plate has a planar area.
[0009] In order to obtain the pressing action, a pressure can be
exerted on at least one of the two plates, or on both plates, in a
direction perpendicular to the semiconductor wafer. The pressure
according to the properties of the semiconductor material to be
formed is preferably greater than 1 MPa and the temperature
preferably is greater than 600.degree. C.
[0010] The pressing process can be carried out in an inert-gas or
protective-gas atmosphere, for example nitrogen gas or argon gas.
If the semiconductor material to be shaped is a compound
semiconductor, it is possible, in order to prevent decomposition of
the compound semiconductor, to use an atmosphere enriched with an
element of the compound semiconductor during the shaping. By way of
example, if GaAs is used as the semiconductor to be shaped, the
method can be carried out in an atmosphere enriched with
arsenic.
[0011] In the manner according to the invention, it is possible to
fabricate diverse forms such as convex or concave structures in a
round or sharp-edged embodiment. In this case, the entire
semiconductor wafer can be structured at the same time, thereby
ensuring cost-effective mass production.
[0012] With the foregoing and other objects in view there is
provided, in accordance with the invention, a method for
fabricating a light-emitting diode. The method includes the steps
of providing a semiconductor wafer having a semiconductor surface
to be shaped and clamping the semiconductor wafer in-between two
plates. At least one of the plates has a negative form with respect
to a desired form to be formed in the semiconductor surface. The
semiconductor surface is pressed using the two plates at an
elevated temperature, resulting in a structure having at least one
curved depression produced in the semiconductor surface. An active
layer sequence is grown on a section containing the curved
depression. The structure is provided with electrical contacts.
[0013] In accordance with an added mode of the invention, there is
the step of forming the negative form to have convex structures for
producing concave structures in the semiconductor surface.
[0014] In accordance with an additional mode of the invention,
there is the step of growing a Bragg reflector layer sequence
before performing the step of growing the active layer sequence on
the section containing the curved depression. A further Bragg
reflector layer sequence can be grown after the step of growing the
active layer sequence on the section containing the curved
depression resulting in a vertical resonator laser diode being
produced.
[0015] With the foregoing and other objects in view there is
further provided, in accordance with the invention, an apparatus
for shaping semiconductor surfaces. The apparatus includes two
plates. At least one of the two plates has a negative form with
respect to a desired form to be formed in a semiconductor surface
of a semiconductor wafer. A pressing apparatus is provided for
exerting a pressure on at least one of the two plates in a
direction perpendicular to the semiconductor wafer disposed between
the two plates. Dome-shaped structures for distributing a
compressive force are disposed on that side of the two plates which
is remote from the semiconductor wafer.
[0016] In accordance with a further feature of the invention, the
two plates include a first plate having the negative form and a
second plate with a planar area.
[0017] In accordance with an added feature of the invention, the
two plates are formed of a material, and at a shaping temperature,
the semiconductor wafer to be pressed has a lower hardness than the
material of the two plates.
[0018] In accordance with a concomitant of the invention, the two
plates are formed of silicon, metal, or molybdenum.
[0019] Other features which are considered as characteristic for
the invention are set forth in the appended claims.
[0020] Although the invention is illustrated and described herein
as embodied in a method and an apparatus for shaping semiconductor
surfaces, it is nevertheless not intended to be limited to the
details shown, since various modifications and structural changes
may be made therein without departing from the spirit of the
invention and within the scope and range of equivalents of the
claims.
[0021] The construction and method of operation of the invention,
however, together with additional objects and advantages thereof
will be best understood from the following description of specific
embodiments when read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a diagrammatic, sectional view of an exemplary
embodiment of an apparatus for carrying out the method according to
the invention;
[0023] FIG. 2 is an enlarged sectional view showing a press-shaping
process;
[0024] FIG. 3 is an illustration of a concave lenses fabricated by
the method according to the invention; and
[0025] FIG. 4 is an illustration of a vertical resonator
light-emitting diode fabricated by the method according to the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] In all the figures of the drawing, sub-features and integral
parts that correspond to one another bear the same reference symbol
in each case. Referring now to the figures of the drawing in detail
and first, particularly, to FIG. 1 thereof, there is shown an
exemplary embodiment of an apparatus for carrying out the method
according to the invention. In the apparatus, a semiconductor wafer
1 to be shaped is clamped in between two plates 2, 3, of which the
first plate 2 is the shaping plate and the second plate 3 serves
for retaining or supporting the semiconductor wafer 1. The first
shaping plate 2 has a surface structure that constitutes a negative
form of a desired form of the semiconductor wafer 1. As is
illustrated by way of example, a surface structure may have convex
bulges 21 by which concave depressions are intended to be produced
by the shaping process in the semiconductor surface. As is further
illustrated, a pressing apparatus diagrammatically illustrated by
the arrows, can exert a mutually opposite compressive force on the
two plates 2, 3 in a direction perpendicular to the semiconductor
wafer 1, so that the shaping plate 2 with the surface structure 21
is pressed into the semiconductor surface during the pressing
process at an elevated temperature. A total pressure that has to be
expended for this purpose depends on the semiconductor materials of
the semiconductor wafer 1 and the plates 2, 3 and also on the
ambient temperature. The publication titled "GaAs to InP Wafer
Fusing" in J. Appl. Phys., in Vol. 78, pages 4227-4237 from 1995,
by R. J. Ram et al., discloses that pressures above 1 MPa and
temperatures above 600.degree. C. are necessary in the chemical
bonding of two different semiconductor materials, namely GaAs and
InP. It can therefore be expected that the conditions must be
chosen in this way in the case of the method according to the
invention as well. In order to facilitate the process conditions,
at a given shaping temperature, the semiconductor material to be
shaped should have a lower hardness than the plate material.
[0027] FIG. 2 once again illustrates the shaping process, on an
enlarged scale. The atoms of the semiconductor wafer 1 to be
pressed yield laterally under the high pressure and thus form a
negative replica of the surface profile of the shaping plate 2.
[0028] It is advantageous if the compressive force to be expended
at the two plates 2, 3 is distributed as uniformly as possible
between the plates 2, 3. Therefore, the compressive force, as is
indicated by the arrows, is provided essentially along a line
perpendicular to the semiconductor wafer 1. The dome-like
structures 22, 32 are for laterally distributing the
compressive-force action between the plates and are preferably
applied on both plates 2, 3.
[0029] In order to simplify the construction of the pressing
apparatus, it may also be provided that a compressive force is
exerted only on one of the two plates 2, 3.
[0030] Furthermore, it may be provided that the shaping process is
carried out under an inert-gas or protective-gas atmosphere, for
example under nitrogen or argon. If a compound semiconductor is
intended to be shaped, then decomposition of the compound
semiconductor may occur in an undesirable manner during the shaping
process. Therefore, it is advantageous in such cases if an
atmosphere enriched with an element of the compound semiconductor
is produced during the shaping process. During the shaping of a
III-V semiconductor such as GaAs, it is possible, by way of
example, to use an atmosphere enriched with the group V element
(arsenic). Decomposition can be effectively prevented as a
result.
[0031] Depending on the application, the first shaping plate 2 may
be composed of silicon or a metal, such as molybdenum, or other
suitable substances. The shaping plate 2 is processed prior to the
shaping process in such a way as to produce the correspondingly
negative surface profile 21 with respect to the desired surface
profile of the semiconductor wafer 1. For this purpose, etching
processes or other grinding or polishing methods can be used,
depending on the plate material. By way of example, it is possible
to use silicon wafers patterned by dry etching technology, the
wafers containing convex microlenses, in order to produce concave
lens structures in the semiconductor wafer 1 to be pressed.
[0032] An example of a concave lens structure of this type is
illustrated in FIG. 3, which shows a concave microlens 10 produced
from the semiconductor compounds GaP. The microlens having been
produced by the method according to the invention. The microlens 10
essentially has a curved, concave depression 11 shaped by the
method according to the invention. The semiconductor compound GaP
has the advantage that, with an appropriate thickness, it has low
absorption for visible light and is thus virtually transparent and,
in addition, has a very high refractive index compared with glass.
Therefore, as illustrated in FIG. 3, the concave microlens 10
refracts the light rays 5 to a very great extent as they pass
through.
[0033] In a further application, the method according to the
invention can serve for fabricating light-emitting diodes or laser
diodes. In this case, concave structures 30 are produced on the
semiconductor wafer 1 and, on this basis, further process steps for
fabricating the light-emitting diode or laser diode are carried
out. FIG. 4 illustrates a light-emitting diode fabricated in this
way, which uses an n-conducting GaAs substrate 100 as a starting
material, a curved depression 110 having been shaped into the
substrate 100 by the method according to the invention. In a
further process step, a Bragg reflector layer sequence 120 is then
grown epitaxially on at least one section containing the depression
110. An active layer sequence containing an n-doped layer 130 and a
p-doped layer 140 is then grown epitaxially on the structure. The
layer sequence contains a light-generating pn junction 135 at the
interface of the layers 130 and 140. Power is supplied through a
p-type contact 150 fitted on the p-type side and an n-type contact
(not illustrated) fitted on the n-type substrate 100.
[0034] The output radiation radiated downward by the
light-generating pn junction is reflected largely perpendicularly
to the surface by the curved Bragg reflector, thereby producing a
high coupling-out efficiency. However, it is also possible to
dispense with the Bragg reflector layer sequence, so that only the
active layer sequence with the pn junction 135 is grown on the
depression 110 acting as microlens.
[0035] Furthermore, the structure shown in FIG. 4 can, however,
also be developed to form a vertical resonator laser diode. To that
end, it is necessary merely to deposit expitaxially above the
active layer sequence a second Bragg reflector layer sequence for
forming a resonator. Afterward, it is possible to carry out the
structuring of the vertical resonator laser diode using the known
methods of the art.
* * * * *